1. Field of the Invention
The present invention relates to a focal plane shutter for a camera, comprising a front curtain having a plurality of divided blades.
2. Description of the Related Art
Such camera is known that has an arrangement in which light passing through a photographing lens is reflected on the photographing lens-side surface of a front curtain of a focal plane shutter in the camera, the reflected light is received by a photometric light receiving device, and exposure is controlled based on the output from the light receiving device. Also, such camera is proposed that has an arrangement in which preliminary flashing is activated, the flashed light reflected on a subject is again reflected on the photographing lens-side surface of a front curtain of a shutter and received by a light receiving device, and brightness distribution is obtained from the output of the light receiving device.
In order to restrain flare that develops between the film-side surface of the shutter front curtain and the film surface, it is desirable to have the reflectance of the surface of the shutter front curtain set at not more than 2-3%. However, if photometry is to be conducted by receiving light reflected on a surface of such a low reflectance, then, because of low amount of incident light to the light receiving device, a greater light-receiving area is required of the light receiving device to increase the amount of received light, which raises a problem of efforts being disturbed for decrease in size of light receiving device. Also, if the reflectance of the surface of the shutter front curtain is low, an increased amount of the preliminary flashed light is required when measuring the distribution of reflectance of subject field, which results in an increase in the battery power consumption.
Thus, for example, such focal plane shutters have been proposed in U.S. Pat. No. 3,687,026 and Japanese Utility Model laid-open Application (JP-U-SHO-63-150932) that are adapted to prevent the flare that develops between the film-side surface of the shutter front curtain and the film surface by arranging the film-side surface of the shutter front curtain to be of a low reflectance, and, at the same time, are adapted to decrease in the size of light receiving device and decrease the light amount of the preliminary flashing by arranging the photographing lens-side surface of the shutter front curtain to be of a high reflectance.
However, in a focal plane shutter having the front and rear curtains thereof comprising a plurality of divided blades, a problem exists as shown below when adopting the systems described in the references cited above.
In such kind of focal plane shutters, each divided blade of the front curtain rubs against each other on the contact surface because each such divided blade operates while overlapping each other. In order to prevent painting on the surface of the divided blade from peeling due to such rubbing motion between the divided blades, it is desirable to select a material of low reflectance for the material of the divided blade itself, and apply no surface treatment, such as painting, on the film-side surface of the divided blade. In this case, however, a high reflectance surface is required to be formed on the photographing lens-side surface of each divided blade by surface treatment such as painting.
On the other hand, in such kind of focal plane shutters, an opening for exposure is formed between edge surfaces opposed to each other of the front and rear curtains. Thus, in the case that a divided blade of the plurality of divided blades of the front curtain, located at an end of the plurality of divided blades and forming an opening for exposure (hereinafter referred to as the opening-forming blade), has the opening-side edge surface thereof formed to be a surface of high reflectance, an undesired photograph is liable to be taken due to light reflected on such opening-side edge surface entering the film. In order to avoid this, the opening-side edge surface of the opening-forming blade is required to be formed to be a low reflectance surface, by all means.
Therefore, in the case that a surface of high reflectance is to be formed on the photographing lens-side surface of each divided blade, as described above, it is required that either painting of high reflectance is prevented from covering the opening-side edge surface of the opening-forming blade by applying a strict quality control during the manufacturing process of the opening-forming blade, or additional low reflectance painting is applied to the opening-side edge surface of the opening-forming blade after application of the high reflectance painting.
A painting process may be considered in that high reflectance painting is applied so that certain unpainted space is left on and around the edge surface of the divided blade, and, thereby, the opening-side edge surface of the opening-forming blade is not covered by the high reflectance painting. In this case, however, difference in level results between the painted surface and the unpainted material surface on the surface of the blade, which is liable to cause painting to peel off or the blade itself to be damaged due to the edge surface of a blade bumping into the portion of level difference of another blade.